Fix typo

configure.ac

@@ -24,7 +24,7 @@ if test "x$ac_cv_prog_cc_c99" = "xno" || test "x$ac_cv_prog_cc_c99" = "x"; then
 # We might be on RHEL5 with a git checkout and so broken
 # autoconf. Check if CC is gcc and if it bails when given -std=gnu99.
 # If not, use that.  Yuck.
-  if test "x$ac_cv_c_compiler_gnu" = "yes"; then
+  if test "x$ac_cv_c_compiler_gnu" = "xyes"; then
      CC="$CC -std=gnu99"
      AC_RUN_IFELSE(
 	[AC_LANG_PROGRAM([],[[